Dilatometers are analytical instruments that measure the change in volume of a substance due to thermal, physical or chemical processes. Generally, these instruments employ a variable temperature electric furnace in which the test specimen is heated at a programmed rate to a desired elevated test temperature. Conventionally, the test specimen, which commonly is from about 10 to about 50 mm in length, is held within such furnace between a flat surface on a stationary object and an opposing flat surface on a movable object, such as a ceramic pushrod, that extends outside the furnace. Temperature induced changes in the length of the specimen are transmitted through the rod to a dilation sensor, which can be a mechanical, optical or electrical system for amplifying and measuring the change in position of the rod. Conventional instruments are useful for measuring specimen dilation within the range of from ambient temperature to the maximum temperature of the furnace, which commonly is about 1000 degrees Celsius and often is as high as 1500 degrees Celsius or more.
The least complicated dilatometers in common use are those in which the push rod is coupled to a dial gauge and the dilation of a specimen is read directly from that gauge. Such dial gauge dilatometers are simple to use and inexpensive, but generally are suitable only for low to moderately elevated temperature applications that do not demand high precision. According, dilatometers with improved precision may be desired.